O molecules have a distribution of kinetic energy at

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o Molecules have a distribution of kinetic energy at a given temperature (fig 11.5): - Vapor Pressure increases with increasing temperature of a liquid . o The higher the T, the more KE the molecule has to escape the liquid network and vaporize. o Examine a liquid in a closed container at three different temperatures:
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- So what do we mean by equilibrium? In terms of vaporization, equilibrium means the rate of vaporization and rate of condensation have reached a steady state and are the same. See figure 11.6 in your book. Boiling Point: when the partial pressure of a liquid is equal to atmospheric pressure. o As the T of a liquid is raised, the Vapor Pressure also increases. At the B.P., molecules underneath the surface of the liquid being to vaporize, in addition to the molecules at the surface. o Recall our class discussion on atmospheric pressure and “high altitude cooking directions” 11.3 Phase Diagrams - Phase Diagrams are a graphical summary of conditions under which different states of a substance are stable. Phase Diagram for CO 2 - At atmospheric pressure (1 atm or 10 barr), CO 2 (s) sublimes to a vapor as it is heated - At 5.1 atm (51 barr)and -57 °C, CO 2 reaches its triple point : all three phases exist at this T and P. - At 7.3 atm (73 barr) CO 2 reaches its critical point : a true liquid phase no longer exists no matter how high the P is increased. At the ciritical point, the vapor and liquid approach similar densities. - Supercritical CO 2 is used today in many applications including dry cleaning, and extraction of caffeine and other natural products from plant or other sources. It is an ideal green solvent, non-toxic, reusable, etc. This has been used to replace harmful, and sometimes carcinogenic, solvent usage in the above applications. 11.4 Surface Tension and Viscosity
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